1. Field of the Invention
The invention relates to the field of preparation of carbon paper, and more particularly to a method for producing carbon paper based on a differential-pressure rapid CVI (chemical vapor infiltration) coating, and a device related thereto.
2. Description of the Related Art
Carbon paper is a special functional paper, and the preparation method thereof is same as the traditional paper making process and can be roughly divided into a dry method and a wet method. The wet method is mostly studied at present. Specifically, the following methods are mainly adopted for preparing carbon paper.
(1) Mixing a polyvinyl alcohol (PVA) type solution capable of being used as a bonding agent with chopped carbon fibers, shaping on a paper machine by using the papermaking technology, mutually sticking the chopped carbon fibers after drying, impregnating with dilute solution of phenolic resin and other carbonizable substances, and then preparing a base paper material for carbon-bonded carbon fiber by solidification/carbonization process.
(2) Mixing the dispersion medium with carbonizable short fiber with self-adhesive property, mutually sticking the chopped carbon fibers using the carbonizable short fiber after pulping, carbonizing the carbonizable short fiber in inert atmosphere at the high temperature of 1000° C., and then preparing a carbon-fiber porous material with porosity of 60-90% and resistivity of about 0.1 Ω·cm.
(3) Using the chopped carbon fiber and paper pulp as bonding agent as the raw material, and carrying out paper making and paper forming using the papermaking technology. The paper pulp as bonding agent is removed after being oxidized and gasified in the subsequent hydrophobic treatment process, and meanwhile, lots of uniform pores left on the carbon paper have the function of pore-forming material. The processing method is favorable for reducing the manufacturing cost of carbon paper, and the air permeability can be controlled by controlling the amount of the added paper pulp.
Based on the harsh service environment of carbon paper, carbon paper must have various physical properties such as good mechanical and electrical properties, surface property, durability, and pore size and distribution uniformity. In the traditional carbon paper preparation method, resin is generally adopted as the bonding agent of carbon fiber, the carbon fibers are connected with each other by a hot-press method after drying, and then resin becomes glassy carbon after carbonization and graphitization at the high temperature for enhancing the electrical conductivity of carbon paper, because carbon has better electrical conductivity. However, during the process of carbonization and graphitization, resin will be gradually reduced in volume and decreased in density along with the gradual rise of temperature, thus cracking may be caused between the fiber and matrix carbon, and cracks also may appear inside the matrix carbon. The direct consequence of these problems is that the overall electrical conductivity and mechanical properties of carbon paper are seriously reduced, and its durability is also affected.